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Principles of chemical reaction in universities
Summary of the basic knowledge of chemical reaction principle Chapter 1: Material change and energy change in chemical change. 1. The essence of material change: the rupture of old chemical bonds and the formation of new chemical bonds. 2. The essence of energy change: it is necessary to absorb energy to destroy old chemical bonds and release energy to form new chemical bonds. In the process of chemical reaction, the change of matter is inevitably accompanied by the change of energy. Concept of reaction heat: the energy released or absorbed in the process of chemical reaction can be expressed by heat (or converted into corresponding heat), which is called reaction heat; Exothermic reaction: the reaction that releases energy in the process of chemical reaction is called exothermic reaction; Endothermic reaction: The reaction that absorbs energy in the process of chemical reaction is called endothermic reaction. 3. Enthalpy: The physical quantity used to express this inherent energy property of a substance is called enthalpy. Symbol: H 4, enthalpy change of chemical reaction: the change of total energy of reactants and total energy of products during chemical reaction is called reaction enthalpy change. Thermochemical research shows that for chemical reactions under isobaric conditions, if all the energy changes of substances in the reaction are converted into heat energy (possibly accompanied by changes in the volume of the reaction system), but not into other forms of energy such as electric energy and light energy, the reaction heat of the reaction is equal to the enthalpy changes of substances before and after the reaction. Expressed as: Qp=△H, where: Qp represents the reaction heat of chemical reaction under constant pressure. △H=H (reaction product) -H (reactant) △H is the difference between the total enthalpy of the reaction product and the total enthalpy of the reactant, which is called the enthalpy change of the chemical reaction. Pay attention to the method of calculating the reaction heat by bond energy: Δ h = ∑ e (reactant) -∑E (product), that is, the reaction heat is equal to the difference between the sum of bond energies of reactants and the sum of bond energies of products.